Conventionally, as polystyrene porous resins, hydroxystyrene-polyene copolymers (JP-A-52-23193 and JP-A-58-210914) and copolymer resins obtained by copolymerization of alkoxystyrenes, aromatic polyvinyls and aromatic vinyl compounds (JP-A-5-86132) are known. Beads made of these porous resins have been mainly applied to ion exchange resins, absorbents and the like. In these uses, adsorption of the largest possible amount of a substance is considered to be right, and therefore, conventional development guidelines of porous resin beads include attaching as much amount as possible of functional groups and increasing the specific surface area to the highest possible amount, thus aiming toward enhanced ability to adsorb a substance per unit volume of porous resin beads. Moreover, these porous resin beads are used as reaction fields to efficiently carrying out chemical reactions. In this case, to increase the amount of a substance synthesized by chemical reaction, it is preferable to make the porous resin beads swell in an organic solvent to a certain degree. However, when plural organic solvents are exchanged to perform chemical reactions, different degrees of swelling of the porous resin beads in each organic solvent give rise to a problem of, for example, changes in the pressure of the inside of columnar reaction containers having given volumes and the like. Therefore, the development of a porous resin showing smaller changes in the degree of swelling due to the kind of organic solvents has been desired.